The wall unit depth must always be lower than the base unit depth, to minimise the possibility of bumping into the door with your head.
The most common average size hovers around 35 cm, especially in conjunction with a base unit standard depth of 60 cm.

Also in this case, however, it is possible to increase the depth as needed, with custom solutions, while preferably maintaining the offset with the worktop.

How much space is required between base units and wall units?

For wall units, the conventional distance from the base unit is roughly 51/54 cm. In addition, the height of the wall units may also vary: if you have a low ceiling, you may want to exploit the space horizontally by occupying less space on the walls using shorter wall units. On the other hand, if you have a tall ceiling and a small room, you may choose to have a double row of wall units or a full-height wall unit.

How deep must the base units be?

The conventional depth for the base units and worktop is roughly 60 cm.

However, a greater depth tends to be a more practical and functional solution, as a deeper worktop improves visibility and ensures a larger support surface.